To study the suppressive mechanism of myelin antigen-specific autoreactive T cells in the periphery, we have generated transgenic (Tg) mice expressing Myelin Basic Protein (MBP)-specific human T cell receptor (TCR) isolated from an MS patient. Since conventional myelin antigen-specific TCR Tg mice were generated from encephalitogenic T cell clones, the Tg mice generated from the encephalitogenic TCR developed spontaneous or active EAE. However, it is impossible to identify encephalitogenic T cell clones from humans. We chose the T cell clone which recognize the immunodominant epitope of MBP, MBP111-129, in humans expressing the HLA-DRB1*0401. Interestingly, CD4+CD25- Tg Tcells can differentiate into Th1 cells in vitro and the Th1 cells induce EAE upon adoptive transfer, while EAE cannot be induced in the MS2-3C8 TCR Tg mice by immunization with MBP111-129/CFA. This preliminary experiment suggests that Tregs capable of suppressing the differentiation of encephalitogenic T cells develop in the MS2-3C8 TCR Tg mice. We found that MHC class II-restricted MBP-specific CD8+ Tg T cells develop together with CD4+ Tg T cells in the MS2-3C8 Tg mice. The CD8+ Tg T cells are cytotoxic and produce a high amount of IFN-? in response to MBP111-129/HLA-DRB1*0401 complexes and exhibit Tc1 phenotype. We also found that 8-12% of CD4+ Tg na[unreadable]ve T cells express CD4+CD25+ Foxp3+ phenotype in the MS2-3C8 Tg mice and these Tg Tregs suppress the proliferation of CD4+ CD25-Tg T cells. These CD8+ Tg T cells and CD4+CD25+ Tg T cells are candidate Tregs which suppress the induction of active EAE. In this study, we will identify the regulatory T cell subsets which can suppress active EAE and investigate their suppressive potential against EAE induced by other myelin antigens, PLP and MOG. This study could lead to a better understanding of Tregs and their suppressive mechanism and a solid ground for a NIH RO1 application. 1 Principal Investigator/Program Director (Last, First, Middle): Ito, Kouichi Project narrative The MS2-3C8 MBP-TCR Tg mice, which express HLA-DRB1*0401 and MBP111-129 specific TCR, were resistant to active EAE. The regulatory T cells involved in the protection from active EAE will be analyzed. 1 [unreadable] [unreadable] [unreadable]